Control system for a multiplicity of muffle burners

ABSTRACT

The air flows through the outer annular ducts of the muffle burners and are controlled via the slidable sleeves which are moved in accordance with the load as measured in the air header and a preset value of the load. Also, should the differential pressure change between a point upstream of the swirl means in the inner duct and a point downstream of the swirl means, a controller changes the blower speed to compensate for the change in differential pressure.

United States Patent Sharan 1 Mar. 14, 1972 [54] CONTROL SYSTEM FOR A [56] References Cited IPLI ITY O MULT C F MUFFLE BURNERS UNITED STATES PATENTS [72] Inventor: Harendra Nath Sharan, Seuzach, Zurich,

Switzerland V 3,486,834 12/1969 Frey et al ..43l/l9 [73] Assignee: Sulzer Brothers, Ltd., Winterthur, Switzer- Primary Examiner-Carroll B. Dority, Jr.

land Attorney-Kenyon & Kenyon Reilly Carr & Chapin [22] Filed: Nov. 16, 1970 [57] ABSTRACT [21] Appl 89563 The air flows through the outer annular ducts of the muffle burners and are controlled via the slidable sleeves which are 30 Foreign Application p i i Data moved in accordance with the load as measured in the air header and a preset value of the load. Also, should the dif- Nov. 17, 1969 Switzerland ..17026/69 feremial pressure change between a point upstream f the swirl means in the inner duct and a point downstream of the U-S- wirl m ans a controller changes the blower speed to com- ..F23n pensate f the change in diff ti l pressure [58] FieldoiSearch .43l/19, 89

6 Claims, 1 Drawing Figure PAIENTEUMAR 14 m2 3. 649. l 55 l/l/l/ Inventor: Hana/am #4111 51mm JITORNE Y3 CONTROL SYSTEM FOR A MULTIPLICITY F MUFFLE BURNERS This invention relates to a control system for a multiplicity of muffle burners connected to a common supply.

Muffle burners have been known in which a pair of concentric annular ducts have been provided for imparting a swirling effect to a flow of fuel in order to obtain intensive combustion of the fuel. In some instances, the flow cross section a the inlet to the outer duct has been varied so as to accommodate changes in load while the inner duct has been subjected to constant flows.

Generally, where these muffle burners have been used on an individual basis, the controls required to adjust to different loads have been relatively simple. However, when these muffle burners have been used on a multiple basis and have been connected to a common supply conduit for combustion air, the proposed controls have tended to be complex and expensive.

Accordingly, it is an object of the invention to provide a simple control means for controlling the flow of combustion air from a common source to a multiplicity of muffle burners.

It is another object of the invention to distribute the air for combustion to a plurality of muffle burners uniformly even where the conduits to each muffle burner are of varying resistances.

It is another object of the invention to ensure a substantially constant air exit speed from each inner duct of each muffle burner of a plurality of muffle burners over an entire load range.

Briefly, the invention provides a control system for at least a pair of swirl-type muffle burners wherein each muffle burner has at least two coaxial concentric ducts for parallel flow of combustion air and wherein each muffle burner is connected to a common supply conduit for the combustion air which conduit has a blower connected thereto. The control system includes a controller for each burner and a final control element which is connected with the outer duct of the burner. Each controller receives a load-dependent set-value and a measured value of the amount of air flowing to the associated burner and acts on the final control element to adjust the control element so as to control the air supply to the outer duct of the associated burner. The system also includes another controller which is arranged to control the pressure difference between a first point situated between the swirl-imparting means in the inner duct of one of the burners and the blower, and a second point situated downstream of the swirl-imparting means. This second controller serves to control the amount of air delivered by the blower.

By means of the control system, a substantially uniform air distribution to all the burners is obtained over a wide range of loads with a substantially constant air exit speed from the inner duct of each burner. Any varying resistances in the air supply branch conduits, such as may occur as a result of the physical arrangement of the burners, affect only the distribution of the air between the inner and outer annular ducts but do not substantially affect the amount of air flowing through the burner. Therefore, there is optimum combustion efficiency over a wide range of load.

These and other objects and advantages of the invention will become more apparent from the following detailed description and appended claims taken in conjunction with the accompanying drawing in which:

The drawing diagrammatically illustrates a control system for two swirl-type muffle burners, one of which is shown in partial section.

As shown in the drawing, two swirl-type muffle burners 2 and 3 are secured by suitable means (not shown) to a wall 1 which, for example, bounds a combustion gas flue of a steam generator. Each of the burners 2, 3 has a ceramics-lined muffle 4, the exit aperture of which discharges at the right hand end, as viewed, into the combustion gas flue bounded by the wall 1 without any constriction in the connection. Each muffle 4 cooperates with a burner lance 11 which is disposed concentrically of the muffle axis and is surrounded by two coaxial annular ducts 6 and 7 leading into the muffle 4. Each annular duct 6, 7 is provided with a swirl means 8, 9 at the exit end which impart a swirl to air flowing through the duct from left to right. The walls bounding the two annular ducts widen out trumpet-fashion at their inlet ends. A sliding sleeve [2 is provided at the inlet end of the outer annular duct 6 to enable the inlet cross section thereof to be varied. The burner lance 11 and the annular ducts 6 and 7 of each burner are surrounded by an air chamber 5 and an air supply branch conduit 20 connects each chamber 5 to a common header 21 provided with an air blower 22. t A throttle point 25 is provided in each header 20 and a differential pressure measuring member 26 of a control system is connected at each point 25 to determine the amount of air flowing to each burner 2, 3. The control system also includes a controller 27 which is provided for each burner and is connected via a single line 39 to the measuring member 26 of the associated burner so as to receive a signal therefrom cor-- responding to the measured value of the amount of air flowing through the associated conduit 20. In addition, each controller 27 receives a set-value signal which is supplied from a load transmitter 30 via a signal line 40. The output signal of each controller 27 which results from a comparison of the measured value signal and the set value signal, e.g., the difference between the signals, influences the amount of air flowing through the outer annular duct 6 of the associated burner by varying the position of the sliding 'sleeve 12 which acts as the final control element. To this end, the sliding sleeve 12 is mounted in the air chamber 5 by means of a pair of parallel linkages one on each side, only that linkage situated behind the sectional plate being visible in the drawing. This rear linkage is connected to the front linkage by two spindles l5, 16 in a suitable manner. Spindle 16 projects from the air chamber 5 and is provided on the front end with a worm wheel 17 which cooperates with a worm 19 mounted on the shaft of an electric motor 18 disposed outside the chamber 15. The worm I9 is driven by the electric motor 18 in dependence the output signal of the controller 27 which is supplied along a suitable line 41.

in addition to the two controllers 27, the control system includes a controller 31 which is common to both the burners 2, 3 and which controls the pressure difference between a first point situated between the swirl means 9 in the inner annular duct 7 and the blower 22, and a second point situated downstream of the swirl means 9 in the inner annular duct 7, in this case in the combustion gas flue. To this end, a differential pressure measuring member 32 is connected to the air chamber 5 of one burner 3 and to the combustion gas flue bonded by the wall 1 so as to measure the pressure differential therebetween and deliver a measured value signal corresponding thereto to the controller 31. The controller 31 also receives a set-value signal from the load transmitter 30 via a signal line 43 and compares the measured value signal to the set value signal in a suitable manner to obtain an output signal. The output signal is emitted through an output of the controller 31 to the blower 22 via a signal line 42 so that the differential pressure is controlled by varying the delivery of the blower 22.

Alternatively, instead of using a differential pressure measuring member 32, it is possible to use a pivot tube mounted in one of the inner annular ducts 7.

The burner lances 11 are connected to a common fuel supply conduit 10 containing a valve 37 which is adjusted by a controller 35. This controller 35 receives a measured value signal from a fuel flowmeter 36 connected into the supply conduit l0 and a set-value signal from the load transmitter 30 via a signal line 45.

When the burners 2 and 3 are operating, the burner lances l 1 receive substantially equal quantities of fuel which may oil or gas or a mixture of both. The air for combustion flows into the air chamber 5 of each burner via the branch conduits 20 and is divided between the annular ducts 6, 7 in the air chamber 5. The air flows entering the two annular ducts 6, 7

lOl077 min receive a helical movement in the swirl-imparting means 8, 9 and this helical movement results in an intensive combustion of the fuel in the muffle. The combustion, which takes place with a slight excess of air equal to about 102 percent of the stoichiometrical requirement, is substantially adiabatic, since there is practically no heat loss to the exterior. The combustion is then completed in the muffle 4 of each burner. The proportional distribution of air between the annular ducts 6, 7 in the air chamber 5 depends upon the position of the sliding sleeve 12. The exit speed of the air flowing through the inner annular duct 7 is maintained substantially constant over the entire load range, while the exit speed of the air flowing through the outer annular duct 6 increases approximately linearly as the load increases.

If the load transmitter 30 is set to a higher load, eg, via a suitable handwheel, the two controllers 27 receive a higher set-value which results in an opening movement of the sleeves 12. During this movement, the pressure in each air chamber 5 drops, so that the differential pressure measuring member 32 detects a smaller pressure difference. The controller 31 then increases the delivery of the blower 22 via the signal line 42 to a value corresponding to a new load. Together with the increased set-value for the controllers 27, the set-value of the fuel controller 35 is also increased, so that the amount of fuel is increased in the same direction as the amount of air. In this way, the total amount of air can always be distributed uniformly to the burners and at the same time substantially constant exit speed can be obtained for the air flowing through the inner annular duct 7. This prevents a higher static pressure at the entry of the branch conduit to the burner 2 (as compared with the static pressure at the entry of the branch conduit 20 to the burner 3) from resulting in a corresponding higher air flow for that burner 2.

it is noted that the higher static pressure produced by deceleration of the air at the end of the conduit 21 only has the effect that the throughput through the inner annular duct of the burner 2 is proportionately somewhat higher than through the inner annular duct of the burner 3; however, this has no effect on the quality ofcombustion.

lt is also noted that a control system similar to the above can be used where there are more than two turbulent muffle burners, in which case, an additional controller 27 is provided for each additional burner.

Further, if the burners have three coaxial ducts instead of two, then it is possible to provide only the outer one of the three ducts with the final control element or, alternatively, each of the two outer ducts of the three may be provided with a final control elementuln either case, at least the innermost duct is left free of any final control element.

What is claimed is:

1. A control system for at least two swirl-type muffle burners connected to a common supply conduit for supplying combustion air to said burners, each said burner having a least two coaxial ducts for conveying parallel flows of combustion air; each duct having means therein for imparting a swirl to the flow of air flowing therethrough, a control element connected to the outer of said ducts for controlling the flow of air to said outer duct, and a blower for supplying air to said conduit; said control system including a pair of first controllers, each controller receiving a load dependent set value and being connected to a respective burner to receive a measured value of the amount of air flowing to said burner, each controller being connected to said control element of said respective burner to adjust said control element in response to a differential between said set value and said measured value to control the flow of air through said outer duct; and

a second controller connected between and to a first point located between said blower and said swirl-imparting means in the inner duct of one of said burners and a second point located downstream of said swirl-imparting means for measuring a pressure difference between said goints, said second controller being connected to said lower for controlling said blower in response to a predetermined pressure difference between said points to control the amount of air delivered through said blower.

2. A control system as set forth in claim 1 wherein said first point for measuring the pressure difference is located downstream of the measuring point for supplying said measured value of the amount of air flowing to one of said burners.

3. A control system as set forth in claim 2 wherein said burners lead into a common combustion gas flue and wherein said second point for measuring the pressure is located in said gas flue,

4. A control system as set forth in claim 3 which further includes means for supplying a load dependent set value to said second controller.

5. A control system as set forth in claim 1 wherein said burners lead into a common combustion gas flue and wherein said second point for measuring the pressure is located in said gas flue.

6. A control system as set forth in claim 1 which further in cludes means for supplying a load dependent set-value to said second controller.

in in 

1. A control system for at least two swirl-type muffle burners connected to a common supply conduit for supplying combustion air to said burners, each said burner having at least two coaxial ducts for conveying parallel flows of combustion air; each duct having means therein for imparting a swirl to the flow of air flowing therethrough, a control element connected to the outer of said ducts for controlling the flow of air to said outer duct, and a blower for supplying air to said conduit; said control system including a pair of first controllers, each controller receiving a load dependent set value and being connected to a respective burner to receive a measured value of the amount of air flowing to said burner, each controller being connected to said control element of said respective burner to adjust said control element in response to a differential between said set value and said measured value to control the flow of air through said outer duct; and a second controller connected between and to a first point located between said blower and said swirl-imparting means in the inner duct of one of said burners and a second point located downstream of said swirl-imparting means for measuring a pressure difference between said points, said second controller being connected to said blower for controlling said blower in response to a predetermined pressure difference between said points to control the amount of air delivered through said blower.
 2. A control system as set forth in claim 1 wherein said first point for measuring the pressure difference is located downstream of the measuring point for supplying said measured value of the amount of air flowing to one of said burners.
 3. A control system as set forth in claim 2 wherein said burners lead into a common combustion gas flue and wherein said second point for measuring the pressure is located in said gas flue.
 4. A control system as set forth in claim 3 which further includes means for supplying a load dependent set value to said second controller.
 5. A control system as set forth in claim 1 wherein said burners lead into a common combustion gas flue and wherein said second point for measuring the pressure is located in said gas flue.
 6. A control system as set forth in claim 1 which further includes means for supplying a load dependent set-value to said second controller. 